Dosing Pump Maintenance: Diaphragm, Valve Set, Degassing, and Calibration
Maintenance steps, wear part service lives, troubleshooting symptoms, and calibration procedures compiled from Iwaki dosing pump manuals.
Three Rules of Maintenance
- Replace whenever the head is disassembled: the diaphragm, O-ring, and valve set are replaced together (EWN-R, EWP, EH-E manuals).
- Track service life by hours: the estimated service life of the valve set and diaphragm for EWN-R, EH-E, and EWP is 8,000 hours; values for IX and LK are in the table below.
- Degas and calibrate after every intervention: air is bled from the pump after maintenance, and flow rate is measured under actual line conditions.
Part Service Life and Replacement Intervals
| Series | Part | Estimated life (manufacturer) | Note |
|---|---|---|---|
| EWN-R, EWN-A, EWN-Y | Valve set (2 sets), diaphragm, automatic air vent valve set (type A) | 8,000 hours | Clean water, ambient temperature, continuous operation |
| EWP | Valve set (2 sets), diaphragm, O-ring | 8,000 hours | Replaced at every disassembly |
| EH-E | Valve set (2 sets), diaphragm, O-ring | 8,000 hours | Replaced at every disassembly |
| IX (B007/B015 TC, TE, S6) | Valve set (suction and discharge, 2 sets) | 8,000 hours or 1 year | Diaphragm and valve set replaced when head is disassembled |
| LK-F | Valve, valve guide, valve seat, valve gasket, O-ring | 12 months | O-ring replaced at every disassembly |
| LK-F | Diaphragm | 4,000 hours | Inspect every 6 months in light duty; replace if cracked or deformed |
The manuals note that service life varies depending on the properties of the pumped liquid, temperature, and pressure. Keeping a spare wear-part kit on hand is recommended; the diaphragm and valve set are determined by the model code.
Symptom, Cause, and Remedy
| Symptom | Possible cause | Remedy (EWN-R manual) |
|---|---|---|
| Pump does not run (LED off, blank screen) | Supply voltage too low; no power to pump; broken wire | Check allowable 90–264 VAC range; correct switch and wiring; replace broken wire |
| No liquid pumped | Air lock in pump; stroke length too short; air entering suction line; valve set upside down; missing valve gasket; foreign matter in valve; ball stuck to seat | Degas; set stroke length to 100 percent and adjust; correct piping; reinstall valve set; install gasket; disassemble and clean valves, replace if needed |
| Flow rate fluctuates | Air in pump head; overfeeding; foreign matter in valve; ruptured diaphragm; pressure fluctuation at injection point | Degas; install check valve; clean valves; replace diaphragm; improve piping layout |
| Liquid leaks | Loose fitting or air vent body; loose pump head; missing O-ring or valve gasket; ruptured diaphragm; excessive discharge pressure | Tighten; torque pump head to specification; install O-ring and gasket; replace diaphragm; verify discharge line is not closed or clogged |
| Key operation ineffective | Key lock active | Release key lock |
| External signal not received | Signal not reaching pump; EXT mode programming incomplete | Check wiring; complete programming and press start/stop key |
Daily and Periodic Checks
- Daily: whether liquid is being pumped, normal suction and discharge pressure, deterioration, crystallization, or precipitation of the liquid, abnormal noise and vibration, and air ingress at head connections and the suction line.
- Pump head bolts: plastic parts creep under temperature changes and bolts may loosen. For the EWN-R, retighten every three months in a diagonal sequence to uniform torque.
- Check valve: clean or replace periodically to prevent crystal clogging.
- LK-F: inspect the valve assembly every 6 months; change the gear oil once a year (0.22 liters for LK-F, using the gear oil recommended in the manual), or immediately if the oil has emulsified.
| Model | Head bolt torque | Bolt |
|---|---|---|
| EWN-B09, B11, B16, B21, C16, C21 | 2.16 N·m | M4 hex socket |
| EWN-B31, C31 | 2.55 N·m | M4 hex socket |
| EWN-C36 | 2.55 N·m | M5 hex socket |
| EWP-038B, 080C, 130D | 2.16 N·m | M4 hex socket |
| EWP-270E | 2.55 N·m | M4 hex socket |
| EWP-410F, 420F | 2.55 N·m | M5 hex socket |
If a torque wrench is not available, the EWN-R manual describes tightening the bolt as far as possible by hand using the long arm of the hex key, then turning the bolt an additional 90 degrees clockwise using the short arm.
Valve Set and Diaphragm Replacement (EWN-R Example)
The sequence below is from the EWN-R manual; other series follow similar principles but must be serviced according to their respective model manuals. Wear eye protection, chemical-resistant gloves, a mask, and a face shield during work; disconnect power to the pump and relieve pressure in the discharge line before starting.
1. Relieving pressure
- Stop the pump.
- Open the air vent port by turning the adjusting screw two turns counterclockwise; do not turn three turns or more, as liquid may come out around the adjusting screw.
- Verify that liquid flows from the air vent port and that pressure is relieved; if no liquid flows, run the pump until pressure is relieved.
2. Discharge valve set
- Loosen the union nut and remove the discharge and air vent tubes.
- Turn the lock nut counterclockwise to remove air vent body A, then remove body B with a 21 mm socket wrench.
- Pull out the valve set with tweezers; insert the new set and screw in body B with the lock nut. Do not install the set upside down or in the wrong order, as this causes leakage or reduced flow; do not forget the O-rings and gaskets, and keep the set free of dust and foreign matter.
- Reinstall body A and connect the tubing.
3. Suction valve set
- Disconnect the suction tube from the union nut and remove the fitting with a wrench.
- Pull out the valve set with tweezers (do not drop it).
- With the new set in place, tighten the fitting fully by hand, then tighten an additional quarter turn with a wrench and connect the tube.
4. Diaphragm
- Run the pump, set the stroke length to 0 percent, and stop the pump.
- Remove the tubing and unbolt the pump head with a hex key.
- Unscrew the diaphragm from the plunger by turning it counterclockwise; transfer the retainer and diaphragm spacer(s) onto the stud of the new diaphragm. The number of spacers varies by model — do not lose them. The rounded edge of the retainer faces the diaphragm.
- Screw the diaphragm onto the plunger until it bottoms out; set the stroke length to 100 percent and stop the pump.
- Install the pump head and tighten the bolts in a diagonal sequence to the torque specified in the table.
Degassing and Recommisioning
Normal performance cannot be achieved until gas is bled from the pump. The EWN-R manual requires degassing in the following situations: initial start-up, when flow rate is too low, after changing the liquid in the tank, after a long shutdown, and after maintenance or inspection.
- Route the end of the air vent tube back to the tank or into a container; gas and chemical are discharged together.
- Turn the adjusting screw two turns counterclockwise.
- Run the pump at maximum stroke rate (100 percent stroke rate, AUX signal, or pressing the UP and DOWN keys simultaneously).
- Run for more than ten minutes, then stop the pump and close the screw clockwise.
- Verify that liquid is being pumped and that connections do not leak; if liquid is not being pumped, repeat the degassing procedure.
On the automatic degassing type (EWN-A), this procedure is not required as long as the air vent valve operates; if an air lock forms, the same method is applied. The manual requires keeping suction lift at 1 m or less on the automatic degassing type, otherwise the valve may not function. For off-gassing chemicals, flooded suction (suction tank above the pump) is recommended. When stopping the pump, always stop it via the key and wait three seconds before unplugging it, otherwise the last stop command may not be saved to memory.
Flow Rate Calibration
Calibration determines the volume pumped per stroke; the flow rate displayed on the screen is calculated from this value. Manufacturers require calibration to be performed on the actual piping at the set stroke rate and stroke length, otherwise accuracy decreases.
EWN-R
The pump is run for one minute under actual operating conditions and the pumped volume is measured. The pump is placed in manual wait state, the DISP key is held for three seconds to enter calibration mode, and the measured flow is entered and saved. Flow adjustment is made via stroke rate rather than stroke length.
EWP
Output capacity per stroke is calculated by dividing the pumped liquid volume by the number of strokes. Calibration is performed on the actual pipeline at the set stroke rate and stroke length.
IX
A calibration cylinder is connected to the suction line; the calibration tube is not submerged in the liquid inside the cylinder. A wait time of 10–999 seconds and a stroke count of 60–120 are selected, and the drawn-down volume in the cylinder is entered. For viscous liquids, suction speed is reduced.
In the IX-B series, volume per stroke is, for example, 0.6 mL for B007, 1.3 mL for B015, 2.5 mL for B030, and 3.8 mL for B045. For continuous verification of actual flow rate, an EFS electromagnetic flow sensor is mounted on the discharge of an EWN-Y pump; the pump automatically adjusts its stroke rate according to the measured flow.
Additional Notes for LK and IX
- LK-F: a differential pressure of at least 0.3 bar is required on the discharge line; if absent, a back-pressure valve is installed. A pulsation dampener (accumulator, air chamber) is recommended; if the air chamber is non-bladder type, the air dissolves into the liquid over time and is replenished periodically. Before a long shutdown, retract the diaphragm shaft completely; during shutdown, run the pump for approximately 5 minutes at zero discharge pressure every three months to lubricate the motor bearings. After several months of shutdown, flow rate may initially be low due to diaphragm deformation and recover after several hours of operation.
- IX: do not plug the drain port; liquid in the drain pan indicates a damaged diaphragm. The flow rate on the calibration screen is calculated. Tighten head bolts in a diagonal sequence to the torque specified in the manual.
See dosing and chemical pumps, Iwaki pumps, magnetic drive pumps, and polymer dosing pumps for pump selection and related guides.
Frequently Asked Questions About Dosing Pump Maintenance
Wear part service life, flow issues, leakage, calibration, and the IX drain port.
When are the diaphragm and valve set replaced on a dosing pump?
The Iwaki EWN-R, EH-E, and EWP manuals specify an estimated service life of 8,000 hours for the valve set (2 sets), the diaphragm, and (on type A) the automatic air vent valve set. In the IX series, 8,000 hours or 1 year is specified for the valve set; in the LK-F series, 12 months for the valve assembly and 4,000 hours for the diaphragm. These values are based on continuous operation with clean water at ambient temperature; pressure, temperature, and chemicals may shorten service life. Whenever the pump head is disassembled, the diaphragm, O-ring, and valve set are replaced.
The dosing pump is not pumping liquid — what should be done?
The sequence in the EWN-R manual: if there is an air lock in the pump, perform degassing; if the stroke length is too short, set it to 100 percent and then adjust to the required value; if air is entering through the suction line, correct the piping; if the valve set is installed upside down or a valve gasket is missing, reassemble it; if foreign matter is in the valves or a ball is stuck to the seat, disassemble and clean them, replacing if necessary.
What should be checked if the flow rate fluctuates?
Air trapped in the pump head (degassing), overfeeding (requiring a check valve), foreign matter in the valves, a ruptured diaphragm, and pressure fluctuations at the injection point are the primary causes. To keep pressure steady at the injection point, the piping layout or injection location is improved.
Where do leaks occur on a dosing pump?
According to the EWN-R manual, a loose fitting or air vent body, a loose pump head, a missing O-ring or valve gasket, a ruptured diaphragm, and excessive discharge pressure cause leakage. Pump head bolts may loosen due to creep of plastic parts; therefore, they are tightened in a diagonal sequence to the specified torque before initial start-up and every three months.
How is a dosing pump calibrated?
Calibration determines the liquid volume per stroke by dividing the pumped volume by the number of strokes. On the EWN-R, the pump is run for one minute under actual operating conditions and the measured flow is entered in calibration mode. In the IX series, a calibration cylinder connected to the suction line is used; the wait time and stroke count are set, and the drawn-down volume in the cylinder is entered. The flow rate shown on the screen is a calculated value, not a measured one.
What does liquid in the drain pan of an IX series pump indicate?
The IX manual describes the drain port as a safe collection path for leaked liquid if the diaphragm ruptures, and treats liquid in the drain pan as a sign of a damaged diaphragm requiring immediate intervention. The drain port must not be plugged, as it serves as a breather port keeping the pressure behind the diaphragm atmospheric, and the end of the drain tube must not be submerged in the drained liquid.
What information is needed for spare parts?
Iwaki parts lists are organized by model code; the wetted-end material code (e.g., VC, PC, TC, S6) determines the valve ball, valve seat, gasket, and O-ring materials. Sending the model code from the pump nameplate to [email protected] is sufficient.
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